touch the speaker wires to your tongue and measure how high you jump!
with the power output of some of the modern amplifiers, that can actually be quite the alarming experience.
eg, a 1600 watts into 8 ohm class d power amplifier, can swing quite the alarming wave. (betwixt a pair of fingers).
Feel that reggae bass line. literally. muscles just a' flappin' away to the beat....
Ask me how I know....